62.General principles of hormonal regulation. Chemistry of hormones. Storage
and secretion of hormones. Mechanisms of hormonal action.
General principles of hormonal regulation.
The multiple activities of the cells, tissues, and organs of the body are coordinated by
the interplay of several types of chemical messenger systems:
● Neurotransmitters are released by axon terminals of neurons into the synaptic
junctions and act locally to control nerve cell functions.
● Endocrine hormones are released by glands or specialized cells into the
circulating blood and influence the function of cells at another location in the
body.
● Neuroendocrine hormones are secreted by neurons into the circulating blood and
influence the function of cells at another location in the body.
● Paracrines are secreted by cells into the extracellular fluid and affect
neighbouring cells of a different type.
● Autocrines are secreted by cells into the extracellular fluid and affect the function
of the same cells that produced them by binding to cell surface receptors.
● Cytokines are peptides secreted by cells into the extracellular fluid and can
function as autocrine, paracrine, or endocrine hormones.
The endocrine hormones are carried by the circulatory system to cells throughout the
body, including the nervous system in some cases, where they bind with receptors and
initiate many reactions. Some endocrine hormones affect many different types of cells
of the body. Other hormones affect only specific target tissues, because only these
tissues have receptors for the hormone.
Chemistry of hormones. Storage and secretion of hormones.
Hormones are classified according to chemical structure. Chemically, hormones and
neurohormones are of three types:
● Proteins and peptides. Included in this group are peptides ranging from as small
as three amino acids (thyrotropin-releasing hormone) to proteins almost 200
amino acids long (growth hormone and prolactin).
● Steroids. These are derivatives of cholesterol and include the adrenocortical
(cortisol, aldosterone) and gonadal (testosterone, estrogen, progesterone)
hormones.
● Derivatives of the amino acid tyrosine. Included in this group are hormones from
the thyroid gland (thyroxine, triiodothyronine) and adrenal medulla
(epinephrine and norepinephrine).
and secretion of hormones. Mechanisms of hormonal action.
General principles of hormonal regulation.
The multiple activities of the cells, tissues, and organs of the body are coordinated by
the interplay of several types of chemical messenger systems:
● Neurotransmitters are released by axon terminals of neurons into the synaptic
junctions and act locally to control nerve cell functions.
● Endocrine hormones are released by glands or specialized cells into the
circulating blood and influence the function of cells at another location in the
body.
● Neuroendocrine hormones are secreted by neurons into the circulating blood and
influence the function of cells at another location in the body.
● Paracrines are secreted by cells into the extracellular fluid and affect
neighbouring cells of a different type.
● Autocrines are secreted by cells into the extracellular fluid and affect the function
of the same cells that produced them by binding to cell surface receptors.
● Cytokines are peptides secreted by cells into the extracellular fluid and can
function as autocrine, paracrine, or endocrine hormones.
The endocrine hormones are carried by the circulatory system to cells throughout the
body, including the nervous system in some cases, where they bind with receptors and
initiate many reactions. Some endocrine hormones affect many different types of cells
of the body. Other hormones affect only specific target tissues, because only these
tissues have receptors for the hormone.
Chemistry of hormones. Storage and secretion of hormones.
Hormones are classified according to chemical structure. Chemically, hormones and
neurohormones are of three types:
● Proteins and peptides. Included in this group are peptides ranging from as small
as three amino acids (thyrotropin-releasing hormone) to proteins almost 200
amino acids long (growth hormone and prolactin).
● Steroids. These are derivatives of cholesterol and include the adrenocortical
(cortisol, aldosterone) and gonadal (testosterone, estrogen, progesterone)
hormones.
● Derivatives of the amino acid tyrosine. Included in this group are hormones from
the thyroid gland (thyroxine, triiodothyronine) and adrenal medulla
(epinephrine and norepinephrine).
